Have a 72 Skylark, no rust. That's because it was undercoated years ago, I assume in the 70's. Problem is, this undercoating is now like a thick grease? Now matter how hard to wipe it off under the car, it's still there, like it never hardened or cured? Inside the rear quarters, in the trunk, it's like sprayed on grease! Anyone else experience this stuff? Does it wreck the value when going to sell?